This invention relates to a drive system for light vehicles equipped with engines, and more particularly to a drive system which is adapted to transmit the rotation of the engine to the driving wheel(s) through a friction roller during normal operation of the engine, and to transmit the rotation of the driving wheel(s) to the engine through the friction roller to start the engine.
In light vehicles such as bicycle-type motorcycles, i.e. bicycles with compact engines installed thereon, the drive system should desirably be compact in size, light in weight, and inexpensive. To this end, the individual component parts of the drive system should be designed as compact in size and simple in shape as possible, and should be designed so as to facilitate the assemblage and mounting into the vehicle.
However, a drive system of this kind is usually adapted to transmit the rotation of the crankshaft to the drive shaft of the friction roller with speed reduction so as to obtain a large driving force for rotatively driving the driving wheel during normal operation of the engine. According to this drive system, therefore, in starting the engine by rotating the driving wheel through kicking of the pedal, the transmission mechanism of the drive system acts as speed up gears to increase the rotational speed of the crankshaft to a higher speed than the drive shaft of the friction roller. This requires a large pedal-kicking force, making it difficult to achieve smooth starting of the engine.
To avoid such difficulty, there have been used a drive system which employs two separate transmission mechanisms drivingly coupling the crankshaft with the drive shaft, one of which operates during normal operation of the engine, and the other at the start of the engine, respectively, or a drive system in which during normal operation of the engine the crankshaft speed is transmitted from a small-sized pulley on the crankshaft to a large-sized pulley on the drive shaft with a certain reduction ratio, while at the start of the engine the drive wheel rotation is transmitted to the drive shaft through the friction roller by means of a planetary gear, and hence is transmitted to the crankshaft through the above two pulleys. However, while the former drive system is rather complicated in structure, the latter drive system has to be designed large in size due to the use of the large-sized pulley on the drive shaft.